This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. In Gram-negative bacteria, type I protein secretion systems and drug efflux pumps consist of three components: TolC, MacA and MacB. The homotrimeric MacB expels an extremely broad range of antimicrobial compounds to the external medium through the central channel of the outer membrane factor TolC, which spans the outer membrane. The homotrimeric TolC is embedded in the outer membrane as a 12-stranded [unreadable]-barrel. MacA perform as a linker between MacB and TolC. In this project, I will solve the complex structrure of MacA and TolC by EM to reveal the exact mechanism of this drug pumps in detail. This project can contribute to functional studies on drug pump in bacteria resulting in anti-bacterial drug development.